Blender - Automatically reload texts which has changed externally

text_editor_reload_if_modified.py

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bl_info = {
    "name": "Reload if Modified",
    "author": "Dany Lebel (Axon_D), updated by @Andrej730",
    "version": (1,0),
    "blender": (2, 80, 0),
    "location": "Text Editor -> Header Bar -> Reload if Modified",
    "description": "Determine if a text datablock must be reloaded from file in the case that it has changed",
    "warning": "",
    "wiki_url": "http://wiki.blender.org/index.php/Extensions:2.5/Py/Scripts/Text_Editor/Reload_if_Modified",
    "tracker_url": "http://projects.blender.org/tracker/index.php?func=detail&aid=25277&group_id=153&atid=467",
    "category": "Text Editor"
}

# https://archive.blender.org/wiki/index.php/Extensions:2.5/Py/Scripts/Text_Editor/Reload_if_Modified/

"""
This addon will automatically reload a text datablock if its source file
does not corresponds to the last blendfile version. This must be checked
for each file wanted to be updated automatically. It has no effect on internal datablock. 
"""

import bpy


def check_texts_every_second():
    for text in bpy.data.texts:
        if text.is_in_memory:
            continue
        
        if text.is_modified and text.reload_if_modified:        
            # using reloading operators causes crashes, therefore we reload the text manually
            # saving text to file afterwards as it's the only way to flip `.is_modified`
            # since reload doesn't work - https://projects.blender.org/blender/blender/issues/113644
            with open(text.filepath, 'r') as fi:
                new_text = fi.read()
            text.from_string(new_text)
            
            def get_area():
                for screen in bpy.data.screens:
                    for area in screen.areas:
                        if area.type == "TEXT_EDITOR":
                            return area
                        
            context_override = {} 
            context_override["edit_text"] = text
            space = next(space for space in get_area().spaces if space.type == "TEXT_EDITOR")
            context_override["space_data"] = space

            with bpy.context.temp_override(**context_override):
                bpy.ops.text.save()
    return 1 # every second


def draw_header(self, context):
    text = context.space_data.text

    if not text:
        return

    if text.is_in_memory:
        return
    
    layout = self.layout
    row = layout.row()
    row.prop(text, "reload_if_modified")


def register():
    bpy.types.Text.reload_if_modified = bpy.props.BoolProperty(
                            name='Reload if Modified',
                            description=
                            'Automatically reload text file if it has changed',
                            default=False,
    )
    # tried `bpy.msgbus.subscribe_rna(key=bpy.data.texts.path_resolve("is_modified", False))`
    # and didn't worked, therefore going to timer approach as depsgraph update won't be often enough
    # maybe there is more clever way to do this
    bpy.types.TEXT_HT_header.append(draw_header)
    bpy.app.timers.register(check_texts_every_second)


def unregister():
    del bpy.types.Text.reload_if_modified
    bpy.types.TEXT_HT_header.remove(draw_header)
    bpy.app.timers.register(check_texts_every_second)


if __name__ == '__main__':
    register()

I did not see any error messages on blender --debug-all, so I turned to good ol' print debugging. I injected:

import bpy

import logging
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
logger.addHandler(logging.StreamHandler())

def check_texts_every_second():
    logger.debug("reload_if_modified heartbeat")
    ...

and restarted blender with blender --debug-python. I found out that, on blender restart, the heartbeat is there, meaning the scheduled event is running every second. but the moment any project file is loaded, the heartbeat disappeared, with no error messages.

Then if I proceed to disable the add-on, messages come:

        addon_utils.disable text_editor_reload_if_modified
reload_if_modified heartbeat
Traceback (most recent call last):
  File "/home/richardn/.config/blender/4.3/scripts/addons/text_editor_reload_if_modified.py", line 54, in check_texts_every_second
    if text.is_modified and text.reload_if_modified:
                            ^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Text' object has no attribute 'reload_if_modified'

(Update: There is a typo on line 104, register should be unregister xd. But if I made the change, error message on disabling will change into "function not registered", which indicates a same problem: Python context is reset (update update: see below, all timers are cancelled) and register() is not called on project load.)

Then finally I re-enable the add-on,

        addon_utils.enable text_editor_reload_if_modified
reload_if_modified heartbeat
Info: Saved text "<path-to-my-open-script-file-in-my-project>"
reload_if_modified heartbeat
reload_if_modified heartbeat
...

https://blender.stackexchange.com/questions/21034/my-custom-timer-is-cancelled-when-loading-a-blend-file

root cause seems like this (back from 2014 lol)

Alright I made it. Change everything below draw_header() into:

@bpy.app.handlers.persistent
def load_handler(dummy):
    bpy.app.timers.register(check_texts_every_second)


def register():
    # build UI once per plugin load
    bpy.types.Text.reload_if_modified = bpy.props.BoolProperty(
                            name='Reload if Modified',
                            description=
                            'Automatically reload text file if it has changed',
                            default=False,
    )
    # tried `bpy.msgbus.subscribe_rna(key=bpy.data.texts.path_resolve("is_modified", False))`
    # and didn't worked, therefore going to timer approach as depsgraph update won't be often enough
    # maybe there is more clever way to do this
    bpy.types.TEXT_HT_header.append(draw_header)

    # register timer once per plugin load
    bpy.app.timers.register(check_texts_every_second)

    # loading a file cancels all timers, register timer once more per file load
    bpy.app.handlers.load_post.append(load_handler)


def unregister():
    del bpy.types.Text.reload_if_modified
    bpy.types.TEXT_HT_header.remove(draw_header)
    bpy.app.timers.unregister(check_texts_every_second)